This document outlines transitioning to pipelines.
When using 2.0 configuration in combination with pipelines, CircleCI
will inject the CIRCLE_COMPARE_URL environment variable into all
jobs for backwards compatibility. This environment variable is
generated in a different way than the one that is available in legacy
jobs, and is not always available.
It is not injected when there is no meaningful previous revision, which includes the first push of commits to an empty repository, and when a new branch is created/pushed without any additional commits.
There are two main ways of trying out pipelines on a branch without
committing by changing the project-wide setting. One of them is by
using version 2.1 configuration, the other is by including the
experimental stanza.
Note that these methods currently apply to webhooks as well as the version 2 "pipeline trigger" API, but not the version 1.1 "job trigger" API yet. We will announce support for using the version 1.1 API with pipelines soon.
Configuration version 2.1 has always depended on pipelines. We are now enabling pipelines for build requests with version 2.1 configuration automatically, so trying out pipelines on a branch this way only requires upgrading the configuration version.
This also allows use of the 2.1-exclusive features, like pipeline values.
Alternatively there is a configuration stanza which enables pipelines using a version 2.0 configuration:
experimental:
pipelines: true